One possible scenario could be that Clary is in a situation where she has no one around due to some unforeseen circumstances like being stranded in an isolated place. Another could be that she chooses to be alone because she doesn't want others to see her in a vulnerable state during childbirth.
Maybe Simon. If the fanfic takes an alternate path where Clary and Simon end up in a romantic relationship, he could be the father. However, he might be away or unable to be with her when she gives birth.
Well, it could be about the challenges Clary faces during childbirth, like her fear and the support she gets from her friends. Maybe her partner is by her side, holding her hand through the pain.
Obviously, Clary herself is the most important character as she's the one giving birth. Her partner would also be crucial, providing support and sharing the joy of the new arrival.
Obviously, Clary herself is central. Then there's Jace, her love interest. He would be very involved, probably being there for her throughout the pregnancy and during the birth. Simon might also be there. As Clary's best friend, he would offer his support in his own way, perhaps with some comical moments to lighten the mood.
One popular storyline could be Clary's struggle during childbirth. Maybe there are complications, and the other characters in the 'Shadowhunters' world have to come together to support her. For example, Jace could be by her side, freaking out but trying to be strong for her.
Snape would probably use his knowledge of potions. He might have brewed a special pain - relieving potion in advance. He would also use his Occlumency skills to try and block out some of the pain mentally. Since he is a strong - willed character, he would grit his teeth and endure it as best he could while focusing on the task at hand, which is giving birth safely.
One possible plot could be that Snape discovers he has a unique magical ability that allows him to carry a child. He might keep it a secret from everyone in Hogwarts due to fear of ridicule. As he nears the time of giving birth, he would have to find a secluded place within the castle or in the Forbidden Forest. He would endure the pain alone, using his own potions and magic to ease the process as much as possible.
One possibility is that in the fanfiction, she might be in a situation where she has cut herself off from her friends for some noble reason. Maybe she wants to protect them from some dark magic that she believes will target her during childbirth. Another reason could be that she's on a secret mission and has no choice but to be alone when she gives birth.
It could be that the father is an unknown wizard who Harry had a brief encounter with. Maybe it was a one - time magical connection that led to the pregnancy.